1. Field of the Invention
This invention relates to multi-piece solid golf balls comprising a solid core and an enclosing cover of inner and outer layers.
2. Prior Art
At present, golf balls of various structures are known. Among others, a number of patents have been proposed relating to solid golf balls, especially multi-piece solid golf balls having a solid core enclosed with a plurality of cover layers, because of their advantages of distance, controllability or spin rate, and feel (see JP-A 4-244174, 6-142228, 7-24084, 7-24085, 9-10358, and 11-104273).
However, there is still a demand for a multi-piece solid golf ball having further improved flight performance, good spin characteristics, and a pleasant feel when hit with any of wood, iron and putter clubs, as well as improved scraping resistance and durability.
Making extensive investigations in order to meet the above demand, the inventor has found that a multi-piece solid golf ball comprising a solid core and an enclosing cover of inner and outer layers performs better when the solid core has a deflection of at least 1.1 mm under an applied load of 30 kg, the cover inner layer is formed to a Shore D hardness of 45 to 61, the cover outer layer is formed to a Shore D hardness of 35 to 55, and the sum of dimple trajectory volumes each obtained by multiplying a dimple volume by the square root of a dimple diameter is set 530 to 750.
Namely, the invention provides a multi-piece solid golf ball as defined below.
(1) A multi-piece solid golf ball comprising a solid core and a cover which encloses the solid core and consists of inner and outer layers, characterized in that the solid core has a deflection of at least 1.1 mm under an applied load of 30 kg, the cover inner layer has a Shore D hardness of 45 to 61, the cover outer layer has a Shore D hardness of 35 to 55, and the sum of dimple trajectory volumes each obtained by multiplying a dimple volume by the square root of a dimple diameter is 530 to 750.
(2) The golf ball of (1) wherein the cover inner and outer layers each are composed primarily of a thermoplastic resin.
(3) The golf ball of (1) or (2) wherein the cover outer layer is composed primarily of a thermoplastic polyurethane elastomer prepared using an aliphatic diisocyanate.
(4) The golf ball of (3) wherein the cover outer layer contains the reaction product of the thermoplastic polyurethane elastomer with an isocyanate compound as a main component.
(5) The golf ball of (1) or (2) wherein the cover outer layer is composed primarily of an ionomer resin.
(6) The golf ball of any one of (1) to (5) wherein the cover inner layer is composed primarily of an ionomer resin or a resinous component consisting of an ionomer resin and an olefin elastomer.
(7) The golf ball of any one of (1) to (5) wherein the cover inner layer is composed primarily of a thermoplastic polyester elastomer.
(8) The golf ball of any one of (1) to (7) wherein the cover outer layer is made softer than the cover inner layer.
(9) The golf ball of any one of (1) to (8) further comprising an adhesive layer between the cover inner layer and the cover outer layer.
(10) The golf ball of (9) wherein the adhesive layer is formed primarily of an urethane resin base adhesive or chlorinated polyolefin base adhesive to a thickness of 0.1 to 30 xcexcm.
(11) The golf ball of any one of (1) to (10) wherein the solid core has a specific gravity of 1.0 to 1.3, the cover inner layer has a specific gravity of 0.8 to 1.2, and the cover outer layer has a specific gravity of 0.9 to 1.3.
(12) The golf ball of any one of (1) to (11) having a plurality of dimples wherein the elevational cross-sectional shape of the dimple at its center has an area S1, multiplying the dimple diameter by a dimple depth gives an area S2, the average of the dimple cross-sectional shape area ratios represented by S1/S2 is from 0.58 to 0.68, and the total number of dimples is 360 to 540.
The golf ball of the invention has an improved flight performance capability of traveling a relatively low, stretching trajectory, an increased distance, a high degree of control on iron shots, a good feel when hit with any of wood, iron and putter clubs, improved scraping resistance against control shots with an iron club, and improved durability.